Qiu said the team would now scan the brains of their monkeys to try and identifiy circuit deficiencies.

"Once we identify this brain circuit (problem) associated with the autism-like behaviour, we will use therapeutics such as gene editing tools... to manipulate this MECP2 transgene in the transgenic monkey," he explained.

They could then begin to test potential treatments in the macaques - members of the closely-related primate family - a first step towards a possible human drug or therapy.

"Developing sophisticated animal models of autism has always represented a significant challenge for scientists," said James Cusack, research director at the autism charity Autistica.

"This excellent research has developed a more sophisticated model of autism which may further our understanding of autism and could eventually lead to the development of more tailored treatments," he said through the Science Media Centre.

University of California psychiatry professor Melissa Bauman said the work "opens the possibility to explore genetic risk factors in a species more closely related to humans."

Laughs and smiles in chimps turn out to be far more human-like than previously thought and they date to at least 5 million years ago, suggests a new study on chimpanzee facial expressions and vocalizations.
Laughter is not 100 percent identical between the two primates, but people who hear a chuckling chimp usually have little trouble figuring out what the sound generally means.
Chimps go "h-h-h," while humans sound more like "ha-ha-ha" or "he-he-he," said Marina Davila Ross, a senior lecturer in the University of Portsmouth's Department of Psychology and lead author of the study in PLOS ONE.
Then there is the flexibility of the sounds and related expressions.
"Chimpanzees, like humans, can produce their facial expressions free from their vocalizations," Ross explained. "This ability is important for humans. For instance, it allows us to add a smile while talking or laughing, and we can also produce smiles silently. Until now, we did not know that non-human primates also have this ability."
It's even possible that the skills first emerged in the common ancestor of chimps and humans.

In both humans and chimps, facial expressions associated with laughter and happiness usually involve an open mouth with a display of teeth.
"Open mouth expressions, otherwise known as play faces, or as we call them, laugh faces, typically expose the lower teeth by virtue of the mouth being wide or stretched open," co-author Kim Bard, who is a professor of comparative developmental psychology at the University of Portsmouth, told Discovery News.
"We found that there were many types of open mouth expressions, including some configurations with the upper lip drawn up, which sometimes exposes the upper teeth."

Little Callie the chimp, shown in this photo, is enjoying a good laugh with a human friend. Chimps, like people, sometimes laugh and smile when they are alone, too.
"We know that laughter and open mouth faces occur mostly during play, but they can occur in solitary play as well as social play," Bard said. "So our current theory is that laughter (in chimps) is typically associated with feelings of joy."

Both young chimps and children tend to laugh and smile a lot, probably because they play more than adults do (and have less to worry about). But why would teeth be exposed as a sign of friendliness?
Some experts suspect that the open mouth/exposed teeth expression, during non-threatening play times, allows the other individual to learn how to assess others and to adjust their reactions.
Another theory is that a toothy smile often is a visual signal of submissiveness, given that the jaws are usually drawn backward as opposed to the forward thrust of a "grrr" sound and related facial expression.

Since laughter is seen and heard by others, it works wonders as a social bonding tool. In this case, the baby chimp is laughing as its mother tickles its stomach.
The researchers suspect that bonobos, like chimps and humans, also benefit from this type of bonding, and have very flexible facial expressions and vocalizations.

So far, observations of chimps show they are always honest laughers, meaning that the sounds function as true signals of joy.
People, on the other hand, are notorious for fake laughter. We can smile and laugh as though we are happy, even when we're not.
There is, however, a complex twist to chimp laughter: what elicits happiness in some might not in others.
"I've seen adolescent males (chimps) who sometimes exhibit bullying behavior, laughing softly while they are picking on another chimpanzee, who is usually not enjoying the interaction," Bard said. "When the victim gets annoyed enough to try to stop the bullying behavior, then the adolescent can respond with greater laughter, which is even more annoying!"
"So the laughter is 'joyful,'" she said, "but the adolescent finds picking on another chimpanzee, and even their attempt at retaliation, to be something that brings the adolescent some joy."

Studying the origin of laughter and smiles could help researchers better understand disorders such as autism. This condition is characterized, in part, by difficulties communicating via such signals, and in forming relationships with others.
The research also helps us to better understand the abilities of non-human primates, and our evolutionary connections to them. As this image and the one before it show, there's not much difference between a chimp "laugh face" and the typical expression of humans as they enjoy a good guffaw.